[Principles of analysis for sacroiliac joints imaging]

Interpretation of sacroiliac joints imaging is uneasy. Simultaneous erosions, hyperostosis, and ankylosis together make the diagnosis of inflammatory lesions. Articular abnormalities may also be induced by mechanical stress or ligament ossifications. Distribution of the lesions can help to establish a precise diagnosis. Inflammatory lesions may be located in any part of the articulation, including the posterior and inferior part. Mechanical lesions as in osteitis condensans ilii are commonly located in the anterior middle part of the joint. Ligament ossification in case of idiopathic skeletal hyperostosis is located at the margins of joint. The basic for the interpretation of sacroiliac joints is to look at high quality plain radiographs. When diagnosis is uncertain, complementary methods must be considered. CT is useful for analysis of subacute or chronic lesions and MRI is to be preferred for acute lesions, in young patients and when searching for signs of inflammatory activity in an already known chronic disease.